Recovery of metallic values from end-of life lithium polymer batteries and hard disc magnets

Abstract

Recovery of critical metals from e-waste is necessary to alleviate resource scarcity and mitigate supply risk. The present study emphasizes the recycling and recovery of valuable metals Li, Co, Nd, Pr, and Dy from the e-waste components such as lithium-polymer batteries (LIPBs) and hard disk magnets. The present study investigated carbothermal and hydrogen reduction to recover Co and Li from end-of-life (EOL) LiCoO2-LIPBS (LCO-LIPBs). Thermodynamics and kinetics of high-temperature reactions during reduction were studied using thermogravimetric analysis (TGA). Using the iso-conversational approach, the activation energy for the carbothermal reduction of LCO was calculated ~165 kJ/mol. The carbothermal reduction was investigated at 30% in situ graphite dosage in a muffle furnace at 500-900 °C for 1 h, and similar conditions were chosen for the hydrogen reduction. The carbothermal reduction at 900 °C resulted in 61% Li dissolution and 56.2% magnetic yield (74.5 %Co) with a saturation magnetization of 112 emu/g. However, hydrogen reduction at 500 °C yielded much higher Li dissolution (93%) and 57.2% magnetic yield (82.7 %Co) with a saturation magnetization of 104 emu/g. XRD, SEM-EDS, and HRTEM analysis of the reduced powder reaffirm the decomposition of the layered LCO structure and the formation of new phases. Hydrogen reduction favored the formation of LiOH at lower temperatures; however, Li2CO3 was observed at high temperatures and in the carbothermal reduction. Both reductive thermal treatments yield metallic Co, but CoO was also present in the carbothermal reduced powder, which can be attributed to the partial reduction. The present study investigated the complete dissolution grounded NdFeB powder 2M H2SO4, followed by selective Nd precipitation (99%). Also, the influence of various pre-treatment effects on the dissolution of rare earth elements (REEs-Nd, Pr, Dy) and their selectivity was extensively studied. Muffle (850 °C, 1h) and Microwave (auto mode, 850 °C, 10 min) oxidative roasting enhance the REE dissolution (44% and 43%) and their selectivity. However, the hardly soluble NdFeO3 formation limited its dissolution. Chloridizing roasting (CaCl2.2H2O/NdFeB= 2:1, 600 °C, 1.5h) yielded 89% dissolution with Fe dissolution <2%. 100g of NdFeB powder with this recovery approach can yield ~28.5g of REE oxides with a purity of 98%. Another pre-treatment of de-metallization using catalyzed aeration, de-metalized NdFeB alloy powder formed respective hydroxides and their oxides. Prior de-metallization enhanced Nd dissolution to 61% compared to direct leaching and its selectivity. However, after de-metallization, calcination (450 C, 1h) adversely affects the dissolution yet produces a highly Nd-rich leach solution.